Vinblastine and vincristine, periwinkle alkaloids, have been used in the therapy of leukemia, lymphoma and cancer since 1961 (1,2). These drugs depend, for their antimitotic effect, upon crystallization of the cellular microtubules (3). Thus the formation of the mitotic spindle is impaired, and the rate of mitosis of the neoplastic cells is inhibited. However, one of the major problems in utilizing these drugs in patients is infection usually associated with a peripheral neutropenia. The myeloid cells depend for their motility upon an intact microtubule system (4). This motility may also be required initially for release from the bone marrow following maturation, and later for chemotactic responsiveness through solid tissue, phagocytosis of pathogens and perhaps also normal myeloid maturation within the marrow cavity. I propose to study neutrophil motility as measured by steroid stimulated marrow release, epinephrine demargination, Boyden chamber chemotaxis, the Quie test of pathogen phagocytosis and neutrophil biochemistry, in terms of disturbances of the above parameters induced by chemotherapy with Vinca alkaloids. In addition I propose to study the kinetics of the effect of these drugs upon maturing myeloid cells in soft agar marrow culture. The data will provide further insight into the role of microtubules and microfilaments in the kinetics of normal and leukemic myeloid maturation and motility. Vincristine and vinblastine still occupy a prominent position in many of the current protocols for the therapy of both leukemia and lymphoma. Following completion of these studies I propose, using the same techniques, to study the newer drugs such as daunomycin, cytarabine, BCNU and bleomycin as they are developed.